Born Gay

FORUM: PAUL BILLINGS AND JONATHAN BECKWITH

July 1993 Technology Review article

In and era when researchers Have located the genes for conditions such as
Huntington's disease, cystic fibrosis, and Duchenne muscular dystrophy,
some scientists believe that "homosexual" genes will soon be found. It
comes as no surprise, then, that lately the popular press has been humming
with stories about whether homosexuality is genetically determined.

We are uneasy about the current unbridled enthusiasm for studies relating
genes with human behavior. Scientists' arguments for a biological basis for
human differences have previously been used for insidious ends; the
arguments by German scientists before World War II for the genetic
inferiority of Jews is just one example.

Moreover, much of the older scientific analysis of the origins of human
behavior, particularly using biological methods, has been debunked. In the
nineteenth century, for instance, "phrenologists" claimed that they could
predict aspects of an individual's personality, such as sexuality,
intelligence, and criminal tendencies, merely by examining the skull's
structure. Despite its popularity, this "science," which often included
explicitly racist implications, was not based on any reliable evidence.
More recently, after studies in prisons in the 1960s, geneticists jumped to
the conclusion that males with an extra Y chromosome were more likely to be
criminals than other men. Followup studies in the general population showed
that this claim was unwarranted.

But that is the past. It's always possible that the field of human
behavioral genetics has shaken off its tawdry history. Today, when
sophisticated techniques can be used to analyze human DNA, maybe the
renewed interest in connecting biology and behavior portends the
development of a more scientific era. On the other hand, maybe not. A look
at recent studies seeking a genetic basis for homosexuality suggests that
many of the problems of the past have recurred. We may be in for a new
molecular phrenology rather than true scientific progress and insight into
behavior.

Determining Sexual Preference

The first issue to reckon with when conducting studies of homosexuality or
other behavior entails developing a clearcut picture of who exhibits the
trait and who doesn't. This "labeling" problem is exemplified in recent
research of Simon LeVay, a respected neuroanatomist. While at the Salk
Institute in La Jolla, Calif., LeVay did postmortem examinations of the
brains of primarily young male victims of AIDS. In a study published in
Science in 1991, he reported a difference between heterosexual and
homosexual males in the size of the hypothalamus. But he could not really
be certain about his subjects' sexual preferences, since they were dead.
Also, the research design and subject sample did not allow others to
determine whether it was sexual behavior, drug use, or disease history that
was correlated with the observed differences among the subjects' brains.

Even for the living, scientists must decide whether, when trying to
classify a person as gay, to rely on the frequency of homosexual behavior,
the age at which it began, or, as some psychiatrists have suggested, the
presence of homoerotic fantasies. Compounding this difficulty is the
reluctance of many gay people to admit their sexual preference. In this
situation one can easily create inaccurate or inconsistent study groups.

A related problem cropped up in a study by Michael Bailey, a psychologist
at Northwestern University, and Richard Pillard, a psychiatrist at Boston
University School of Medicine. In research published in 1991 in Archives of
General Psychiatry, they reported that among identical twins reared
together, each individual had a high probability (52 percent) of being
homosexual if the other twin was. For nonidentical twins, adopted brothers,
and non-twin siblings, the correlations were much lower (22, 11, and 9
percent, respectively).

The researchers solicited participation for their study through
advertisements in gay newspapers. But this could well have produced a
biased sample. It is not unreasonable to think that identical twins who are
both openly homosexual would be more likely to volunteer for such a study
because of the shared knowledge that they are both comfortable with their
sexuality. Furthermore, if one gay twin "comes out" it might be easier for
the other to do the same.

While the authors interpreted their findings as evidence for a genetic
basis for homosexuality, we think that the data in fact provide strong
evidence for the influence of the environment. On average, both
non-identical twins and non-twin siblings share 50 percent of their genes.
If homosexuality were a genetic trait, the pairs in these groups should
besexual a similar percentage of the time. They certainly should be
homosexual more often than adopted siblings. But Bailey and Pillard's data
do not fit those predictions.

Their results could instead stem from the uniform conditions under which
some identical twins are raised, frequently dressed identically by parents
and viewed similarly by outsiders. The environment could also figure in the
fact that almost half the identical twins did not share sexual preference.

Distinguishing Cause from Effect

Even if one were to accept that these studies indicate a biological
correlation with human behavior, this would not mean that some gene or
brain difference is responsible for that behavior. LeVay admits that the
difference in brain structure he has observed may be due to homosexual
activity rather than a cause of it. Techniques that visualize brain
structure, such as magnetic resonance imaging and position emission
tomography scanning, reveal that the experience of an individual, even as
an adult, can significantly affect brain development. One's emotions,
life's stresses, and numerous other environmental factors can alter the
metbolism ofs the brain and presumably its internal connections.

The problem of distinguishing between cause and effect is perhaps most
clearly illustrated by considering genetics and criminality. There is a
correlation between genes and the likelihood of incarceration in the United
States: a majority of prisoners have inherited dark skin color. But
genetics clearly has nothing to do with the fact that the rate of black
male incarceration has quadrupled over the last four decades, as Troy
Duster, a University of California at Berkiologist, has pointed out.
Rather, racism and the tenuous economic power of so much of the
African-American population likely play causal roles.

Studies of human behavioral genetics could benefit society. But until
geneticists pay more than lip service to the problems in their studies and
the complex interactions of genes and the environment, history may simply
repeat itself.

It is time to hold behavioral-genetics research to higher standards than in
the past, and to recognize that the work is conducted in a society colored
by prejudice, stigma, and discrimination.

PAUL BILLINCS, formerly chief of the Division of Genetic Medicine at
Califomia Pacific Medical Center in San Francisco, is now head of general
internal medicine at the Palo Alto Veterans Administration Hospiral.
JONATHAN BECKWITH is American Cancer Society research professor in the
Department o f Microbiology and Molecular Genetics at Harvard Medical
School.